Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution

N. C Maynard; D. M Ober; W. J Burke; J. D Scudder; M Lester; M Dunlop; J. A Wild; A Grocott; C. J Farrugia; E. J Lund; C. T Russell; D. R Weimer; K. D Siebert; A Balogh; M Andre; H Rème

doi:10.5194/angeo-21-2233-2003

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Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution

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Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution

N. C Maynard, D. M Ober, W. J Burke, J. D Scudder, M Lester, M Dunlop, J. A Wild, A Grocott, C. J Farrugia, E. J Lund, …

Annales geophysicae (1988), Vol.21(12), pp.2233-2258

2003

DOI: 10.5194/angeo-21-2233-2003

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Abstract

Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walén tests, are necessary, but not sufficient, conditions for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the Super-DARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than ~150°. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole ilt angle increases or when IMF BX increases the effective dipole tilt.

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Title: Subtitle: Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution
Creators: N. C Maynard - Mission Research Corporation, Nashua, New Hampshire, USA
D. M Ober - Mission Research Corporation, Nashua, New Hampshire, USA
W. J Burke - Hanscom Air Force Base
J. D Scudder - University of Iowa
M Lester - University of Leicester
M Dunlop - Rutherford Appleton Laboratory
J. A Wild - University of Leicester
A Grocott - University of Leicester
C. J Farrugia - University of New Hampshire
E. J Lund - University of New Hampshire
C. T Russell - University of California, Los Angeles
D. R Weimer - Mission Research Corporation, Nashua, New Hampshire, USA
K. D Siebert - Mission Research Corporation, Nashua, New Hampshire, USA
A Balogh - Imperial College London
M Andre - Uppsala University
H Rème - CESR, Toulouse, France
Resource Type: Journal article
Publication Details: Annales geophysicae (1988), Vol.21(12), pp.2233-2258
DOI: 10.5194/angeo-21-2233-2003
ISSN: 0992-7689
eISSN: 1432-0576
Publisher: European Geosciences Union
Language: English
Date published: 2003
Academic Unit: Physics and Astronomy
Record Identifier: 9984199824602771

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